(1) Field of the Invention
The present invention relates to an amplifier circuit which amplifies a signal from a photodiode, and an optical pickup device.
(2) Description of the Related Art
An amplifier circuit which amplifies a light-receiving signal from a photodiode that receives reflected light from an optical disc is disclosed in Japanese Laid-Open Patent Application No. 10-256841.
FIG. 1 shows a structure of the photodiode amplifier circuit. The photodiode amplifier circuit includes a photodiode PD, an operational amplifier OP, a feedback resistor R10, and a resistor R11. Cs in the diagram indicates stray capacitance. Light which enters the photodiode PD is converted into current by the photodiode PD. The converted current is inputted to a negative input terminal of the operational amplifier OP. The operational amplifier OP and the feedback resistor R10 operate as a current/voltage amplifier which converts current into voltage.